Smoking as a method of food preservation is practised all over the world for various types of food products, especially meat and fish.
However, smoking of milk handling containers like gourds and jerry cans is a practice only common among pastoral communities in Kenya and Ethiopia. It is done to increase the storage life of milk and also to impart a characteristic smoke flavour to not only fresh milk but also fermented camel milk known as suusa. This flavour is highly regarded by the pastoralist communities.
The technique of smoking milk containers is known as Qorasum among the Somali community. The process commonly starts first with the washing and drying of the containers.
A smouldering piece of wood is then inserted into the container and once the smoke has filled the container, it is sealed and only opened when it is ready to be filled with milk. This process only uses wood from specific types of trees.
The most commonly used tree species are Oleaafricana, Acacia totalis, Acacia nilotica, Acacia Senegal, Balanitiesa egyptica and Combretumspp. Some local names in Somali are Kulul and Marer.
Wood smoke has antimicrobial effect against many microorganisms, mainly due to phenol, a chemical in the smoke that destroys the microorganisms.
Smoke also contains different types of chemical compounds such as formaldehyde, acids and alcohols that have varying antimicrobial effects against common milk spoilage microorganisms. These chemicals, in addition to the increased temperature during smoke application, destroy bacterial cells or inhibit their multiplication.
These chemical constituents interfere with either bacterial cell metabolism or transfer of nutrients and other important substances across the cell membrane. The bacterial cell can therefore not undergo nourishment and reproduction which are important processes for survival.
Despite the efforts by pastoralists to reduce milk spoilage by smoking containers, a high proportion of milk reaching the urban markets, especially Eastleigh in Nairobi, is spoiled or fermented (suusa).
This is due to the high temperatures during transportation of the milk and the long distance from the production areas, particularly Isiolo and Garissa. The suusa fetches less money than fresh milk, therefore reducing income of pastoralists.
Milk spoilage can therefore be reduced by first observing proper hygiene during milking and milk handling, using aluminium churns or food grade plastic containers, and chilling milk during transport. This is important in assuring safety of consumers and improving livelihoods of the pastoral communities in Kenya.
The writers are part of The Dairy Team, Egerton University